Bismuth is a common active in over-the-counter liquid pharmaceutical formulations. Pharmaceutical formulations containing bismuth are often sold as suspensions (e.g. Pepto-Bismol®, distributed by Procter & Gamble®), which can be used to treat gastrointestinal symptoms including nausea, heartburn, indigestion, upset stomach, and diarrhea.
It can be difficult to make suspensions, particularly suspensions that are consumer desirable and contain containing insoluble pharmaceutical salts such as bismuth subsalicylate. First, making a suspension with the correct rheology can be difficult. If the rheology is insufficient then the suspension can quickly separate into phases. Furthermore, air bubbles and/or foam can also form during processing, which can also slow batch time, increase waste, and produce a less desirable suspension. Air bubbles can be removed by degassing the suspension over a significant period of time prior to packaging and foam can be removed and discarded from the suspension and also must be cleaned out of the system.
As such, there remains a need for a process for making stable suspensions containing bismuth that reduces batch time and reduces waste by reducing the amount of air that gets mixed into the formulation, while making a suspension that is desirable to consumers.